It is the current practice to coil insulated communication wire in a figure 8 configuration within a box or carton for easy shipment and storage. The figure 8 configuration of the coil is used to reduce twisting of the wire as it is coiled, thereby reducing a tendency of the wire to kink as it is pulled from the carton, generally through an opening in a side wall thereof. The pulling process is facilitated by the installation of a payout tube which extends into the interior of the carton, and which is affixed to a wall thereof in a suitable manner so as to have a stub portion extending outside of the carton. In U.S. Pat. No. 5,152,476 of Moser, there is shown a preferred arrangement for affixing the tube to the wall of the carton having a modified bayonet lock type of action. Numerous prior art arrangements utilize this arrangement, or modifications thereof, for mounting the tube.
Most tubes in use today are in the form of hollow elongated cylinders with the ends thereof being radiused between the outer and inner walls to eliminate sharp corners over which the wire passes as it is pulled through the tube. Such radiused ends are shown in U.S. Pat. Nos. 5,064,136 and 5,115,995 of Hunt. In these arrangements, the entrance end surface substantially conforms to a hemi-toroidal surface having a faired joinder at its inner and outer margins with the inner and outer walls of the tube. Such a rounded surface imposes a lower limit on the bend radius of the wire being pulled through the tube, which however, does not prevent kinking of the wire or damage to its insulation when the wire is being pulled from layers immediately adjacent to the tube and lying between the end of the tube and the wall in which the tube is mounted. In that case, the wire undergoes a sharp reverse bend as it enters the tube, and the radiused end of the tube is insufficient to prevent kinking and possible damage.
The aforementioned Moser patent discloses an end cap for the entrance end of the payout tube which greatly increases the minimum possible radius of curvature of the wire, thereby materially reducing the tendency of the wire to kink even in the extreme reverse bend case discussed in the foregoing. The cap of the Moser patent has, at its entrance or back end an annular flange, the surface area of which conforms to approximately one quadrant of a toroidal surface having a radius of sufficient magnitude that when the wire is bent to pass over the surface in contact therewith, it will not kink. The toroidal surface of the cap is hired into a flat surface, the plane of which is substantially normal to the axis of the cap, and which borders the wire passage interior cylindrical wall surface of the cap. In use, the hollow cylindrical payout tube is mounted in the canon, and the cap is affixed to the entrance end, i.e., the interior or rear end. The wire being payed out cannot be bent to a radius less than the radius of the flange, even for a complete reverse bend, except where the wire passes into the payout tube. At the region where the cap joins the payout tube, there remains a relatively small radius surface over which the wire passes, which allows the wire to be bent to a radius that is too small to prevent kinking, i.e., the radius is less than the critical radius R.sub.c below which kinking can occur.
Any cap arrangement for the payout tube gives rise to the additional problem of the introduction of a separate pan, with the possibility of its being lost or mislaid. Also, the fabrication of such a separate pan requires additional molds and fabrication steps, thereby increasing the cost of the payout tube assembly. Moser apparently recognizes the problem, at least to some extent, by suggesting that the cap and the payout tube may be fused together to produce a single unitary structure, but apparently the two parts are intended to be fabricated separately and then joined, with a consequent two molding operations, hence, an increase in production costs..